1. Field of the Invention
The present invention relates to a motor which is used in CD-ROM drives, DVD-ROM drives, and the like to drive and rotate data recording disks.
2. Description of Related Art
A brushless motor illustrated in FIG. 4 is available as a disk driving motor. The motor comprises a bracket 105, a hub 101 that rotates relative to the bracket 105, a rotor case 107 supported by an inner circumferential surface of the hub 101, and a shaft 102 supporting the hub 101, a sleeve 103 supporting the shaft 102, a stator 106 and a thrust plate 104 positioned to face an end surface of the shaft 102. A joint of the rotor case 107 with the hub 101 is bent along the inner circumferential surface of the hub 101.
As an attempt to reduce vibrations and noise during the driving of the motor, the motor is designed to increase the joining area between the hub 101 and the rotor case 107. That is, the rotor case 107 is bent along the hub 101 to increase the joining area, and using the bent portion the rotor case 107 is joined with the hub 101 to which the shaft 102 is fixed.
This design is, however, insufficient from the viewpoint of reduction of noise associated with the current tendency toward the high-speed rotation of the motor because an overall balance precision of the motor depends on the component precision of individual rotary elements including the hub 101, the rotor case 107, and the magnet 108, and the unbalance of the individual rotary elements with respect to the shaft 102 causes larger vibrations as the speed of motor rotation is increased.
While the hub 101 is directly attached to the shaft 102, the rotor case 107 is joined with the shaft 102 via the hub 101. Since the rotor case 107 is manufactured by pressing, the unbalance of the rotor case 107 with respect to the shaft 102 is likely to occur when the rotor case 107 is joined with the hub 101. In addition, a rare-earth magnet is generally used for the magnet 108, so a clearance exists between the magnet 108 and the rotor case 107 due to tolerance. Therefore, the fixing of the magnet 108 causes unbalance, making it difficult to reduce noise.
The present invention was made in view of the aforementioned problems, and an object thereof is to provide a rotor, a method for assembling a rotor, and a motor using a rotor, which can reduce noise and vibrations without increasing the number of components of the rotor.
A rotor provided in accordance with the present invention is characterized in that a magnet is fixed to a rotor case prior to magnetization. Therefore, it is possible to reduce the number of magnetizing steps during assembly.
A rotor provided in accordance with the present invention is characterized in that positions of a rotor case and a magnet are determined by a centering jig using a rotary shaft as a reference. Therefore, mechanical and electrical unbalances can be extremely reduced, thus lessening noise and vibrations.
A rotor provided in accordance with the present invention is characterized by a first flange portion that extends radially outward form the top end of a cylindrical portion of a rotor case. Therefore, the flange portion does not obstruct assembly of the rotor. Further, it is possible to magnetize the magnet after the magnet is fixed to the rotor case. It is preferable that the first flange portion of the rotor case is brought into abutment with the bottom surface of a hub and fixed thereto by an electrically joining means. This facilitates the fixing of the rotor case to the hub with increased strength.
A rotor provided in accordance with the present invention is characterized by a second flange portion that extends radially inward from the bottom end of a rotor case. The second flange portion determines the axial position of the magnet, and prevents the removal of the magnet. Moreover, the magnet can be set to have an appropriate length (having no waste length) in terms of a positional relationship with a core.
The present disclosure relates to the subject matter contained in Japanese patent application No. Hei. 10-289189 (filed on Oct. 12, 1998), which is expressly incorporated herein by reference in its entirety.